The study is undertaken to determine the occurrence, properties and origin of discoidal vesibles which are characteristic of mammalian transitional epithelium and the persistence of these structures in cultured transitional epithelium before and after neoplastic change, spontaneous or induced, in vitro or in vivo and to search by physical means for evidence of virus production in bladder tumor cells, including cells treated in culture with agents previously found to activate production of RNA viruses. These studies will be correlated with biochemical immunologic evidence of the oncogenic viral genome.